Field of the Invention
The present invention relates to a wafer processing method, and particularly to a so-called TAIKO grinding method.
Description of the Related Art
As a processing method for improving handling easiness of a semiconductor wafer while grinding the semiconductor wafer into a very small thickness, a grinding method is known in which the back surface of the semiconductor wafer corresponding to a device region is ground to form a circular recess and an annular projection is left at the peripheral part (for example refer to Japanese Patent Laid-open No. 2009-176896 and Japanese Patent Laid-open No. 2008-42081). In the present specification, this grinding method is defined as TAIKO grinding. In the TAIKO grinding, after the circular recess is roughly formed by rough grinding, finish grinding is further carried out for the bottom surface of the circular recess by an abrasive with a small grain size for the purpose of enhancing the flexural strength of the device region.
When the finish grinding abrasive collides with the inner circumferential wall of the circular recess formed by the rough grinding, the finish grinding abrasive wears or a crack is caused in the inner circumferential wall. For this reason, the finish grinding abrasive moves down slightly inside the inner circumferential wall and grinds the bottom surface at a finish grinding speed from above at a predetermined distance to the bottom surface. The finish grinding abrasive moves down at a high speed until the position above the bottom surface at the predetermined distance because the finish grinding abrasive does not carry out grinding, and thereby the processing time is shortened.